Fileshares can be a huge security risk. They are vulnerable to ransomware and theft of secrets. If you collaborate with customers, you have to worry about their security practices, too: if they lose control of their access and someone uses it to damage them, they'll still probably blame you.
You can reduce most of this risk by moving to an online fileshare and setting up some simple processes around client access. See the following videos walking through common fileshare scenarios and comparing the security chops of the major vendors. Products are ranked in approximate order of security strength for the average business.
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